MongoDB remove objects from nested arrays based up on the condition using aggregation

Question

I have a nested array, I have to remove the one object , based upon the condition using aggregation

here is the JSON I get from mongodb

{
  "_id":  "633d275ceb34a28755974032",
  "name": "free",
  "products": [
    {
      "title": "Product 1",
      "phone": [
        {
          "title": "Best Phone 1 ",
          "video": {
            "Location": "https://video.mp4"
          },
          "freePreview": true
        }
      ]
    },
    {
      "title": "Product 2",
      "phone": [
        {
          "title": "Best Phone 2",
          "video": {
            "Location": "https://video.mp4"
          },
          "freePreview": false
        }
      ]
    }
    
  ] 
}

But I need the data like

{
  "_id":  "633d275ceb34a28755974032",
  "name": "free",
  "products": [
    {
      "title": "Product 1",
      "phone": [
        {
          "title": "Best Phone 1 ",
          "video": {
            "Location": "https://video.mp4"
          },
          "freePreview": true
        }
      ]
    },
    {
      "title": "Product 2",
      "phone": [
        {
          "title": "Best Phone 2",
          "freePreview": false
        }
      ]
    }
    
  ] 
}

In this data "video object" is removed inside the phone array , because of freePreview is false,

Based upon the freePreview condition , help me to remove the video object

Do you want to delete the data from the document in the collection or just not have it turned in the results? Either way, $map is probably going to be helpful here — user20042973
– user20042973, Commented Oct 6, 2022 at 14:15
I just need a result like db.collection.findOne() using aggregation, can you help me in implement, please share a code — Venkatesh
– Venkatesh, Commented Oct 6, 2022 at 14:20

mickl · Accepted Answer · 2022-10-06 14:25:45Z

You need to use double $map operator to iterate through your array of arrays and use $cond along with $$REMOVE to remove value conditionally:

db.collection.aggregate([
    {
        $addFields: {
            products: {
                $map: {
                    input: "$products",
                    as: "p",
                    in: {
                        title: "$$p.title",
                        phone: {
                            $map: {
                                input: "$$p.phone",
                                in: {
                                    title: "$$this.title",
                                    freePreview: "$$this.freePreview",
                                    video: {
                                        $cond: {
                                            if: {
                                                $eq: [
                                                    false,
                                                    "$$this.freePreview"
                                                ]
                                            },
                                            then: "$$REMOVE",
                                            else: "$$this.video"
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
])

Mongo Playground

Here's a similar example.

rickhg12hs · Accepted Answer · 2022-10-06 15:00:34Z

@mickl's answer works great. If you want to allow for possible document/schema changes, then rather than specifying the fields to keep explicitly, you could use "$mergeObjects" to keep everything and then only modify what you need.

Borrowing heavily from @mickl, here's how you could do that.

db.collection.aggregate([
  {
    $addFields: {
      products: {
        $map: {
          input: "$products",
          as: "p",
          in: {
            "$mergeObjects": [
              "$$p",
              {
                phone: {
                  $map: {
                    input: "$$p.phone",
                    in: {
                      "$mergeObjects": [
                        {
                          "$arrayToObject": {
                            "$filter": {
                              "input": {"$objectToArray": "$$this"},
                              "as": "kv",
                              "cond": {"$ne": ["$$kv.k", "video"]}
                            }
                          }
                        },
                        {
                          video: {
                            $cond: {
                              if: {
                                $eq: [
                                  false,
                                  "$$this.freePreview"
                                ]
                              },
                              then: "$$REMOVE",
                              else: "$$this.video"
                            }
                          }
                        }
                      ]
                    }
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
])

Try it on mongoplayground.net.

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